Not only a corset but a three buckle waist clicher as well. Impressive weapon, slung very low. Perhaps she goes in for the Straight Arm Draw. One thing I learned from the cowboy films in my Saturday Morning Cinema Club days was never shake hands with a left handed draw. Stood me in good stead down the years.
No idea where these are from but from the looks of the photo perhaps an auction?
late 1910s–late 1920s